A Micromegas-based low-background x-ray detector coupled to a slumped-glass telescope for axion research

TL;DR

This paper presents a novel low-background x-ray detection system combining a Micromegas detector with a slumped-glass x-ray telescope, designed for axion research, achieving the lowest background rate in the CAST experiment.

Contribution

It is the first to design and operate an x-ray optic specifically for axion research coupled with a Micromegas detector, advancing detection technology for axion searches.

Findings

Achieved a background rate of 5.4×10⁻³ counts/hour.

First integration of an x-ray optic with a Micromegas detector for axion detection.

Demonstrated improved signal-to-noise ratio in axion search experiments.

Abstract

We report on the design, construction and operation of a low background x-ray detection line composed of a shielded Micromegas (micromesh gaseous structure) detector of the microbulk technique. The detector is made from radiopure materials and is placed at the focal point of a $\sim$~5 cm diameter, 1.3 m focal-length, cone-approximation Wolter I x-ray telescope (XRT) comprised of thermally-formed (or "slumped") glass substrates deposited with multilayer coatings. The system has been conceived as a technological pathfinder for the future International Axion Observatory (IAXO), as it combines two of the techniques (optic and detector) proposed in the conceptual design of the project. It is innovative for two reasons: it is the first time an x-ray optic has been designed and fabricated specifically for axion research, and the first time a Micromegas detector has been operated with an x-ray optic. The line has been installed at one end of the CERN Axion Solar Telescope (CAST) magnet and is currently looking for solar axions. The combination of the XRT and Micromegas detector provides the best signal-to-noise ratio obtained so far by any detection system of the CAST experiment with a background rate of 5.4$\times$10$^{-3}\;$counts per hour in the energy region-of-interest and signal spot area.